A method of this type is known in general as a function of a parking space locating (PSL) system as an assistant to a driver of the vehicle for finding a parking space. In particular the method is known as a function of a parking space measuring system, which supports the driver of a vehicle in searching for a sufficiently large parking space for the vehicle, parking space locating representing a generalization of the parking space measuring system. The parking space measuring system may cooperate with a parking system for semi-autonomous parking in which the driver must operate the accelerator and brake pedals of the vehicle, while steering may also be performed automatically. The system calculates a trajectory for parking the vehicle into the parking space and informs the driver, for example, with the aid of acoustic signals about the actions he has to perform to park the vehicle in the parking space. One basic principle is that the vehicle may not touch, move onto or over a parking space boundary, for example, a curb or already parked vehicles. The more accurately the length of the parking space is detected, the more reliably may a parking maneuver take place.
In addition, a method for ascertaining geometric data for parking maneuvers is known from DE 102 51 558 A1. The lateral distance between the vehicle and a curb is to be measured multiple times successively with the aid of an on-board distance sensor while a vehicle drives past a parking space laterally. Furthermore, the length of the parking space is to be detected via a distance covered while passing by the parking space. Non-parallel passing by the parking space should be compensated for by taking into account a mathematical vehicle model and by detecting an angle between the longitudinal direction of the vehicle and the curb.
German patent document DE 10 2005 015 396 A1 discusses a method in which the position of the lateral parking space boundary facing away from the vehicle to be parked and/or the orientation of the lateral parking space boundary with respect to the vehicle to be parked is calculated from the data detected by the sensor system before reaching and/or after passing the parking space for providing a reliable reference for a lateral parking space boundary. According to a special refinement, the yaw angle between the orientation to be reached by the vehicle in the parking space and an instantaneous orientation of the longitudinal axis of the vehicle to be parked is ascertained, for example, also continuously.
Furthermore, DE 102 20 426 A1 discusses a method for operating a parking assistance system for a vehicle. The vehicle is braked and/or accelerated while moving into and/or out of a parking space by generally taking into account a determination of a length and/or a width of a parking space while the vehicle passes by the parking space. A parking maneuver into the parking space is subsequently determined for the vehicle.
During the following parking maneuver, a future steering angle change is determined on the basis of an instantaneous turn of the steering wheel and communicated to the driver.
In practice, reliably determining the length of a parking space is often found to be relatively difficult if the vehicle passes by the parking space to be determined on a curved trajectory because the distance traveled by the vehicle no longer corresponds to the shortest connecting line between the obstacles delimiting the parking space, i.e., the actual length of the parking space. Rather, the distance traveled may be greater or smaller than the length of the parking space to be determined. This problem is of practical relevance in particular because normally the parking maneuver is initiated by the driver by consciously steering inward.
Measuring the steering angle of the vehicle while driving past the parking space and determining the orientation of the objects delimiting the parking space with respect to the vehicle, comparing the steering angle with the orientation of the delimiting objects, and calculating the length and/or depth of the parking space as a function of the comparison of the steering angle with the orientation of the delimiting objects has also been considered. Such a procedure, however, requires a relatively high computing complexity due to the necessary analysis of signals of different sensors.